1. Field of Invention
This invention relates generally to improvements in operability of vehicular transmissions. More particularly, the invention relates to improvements in transmission shift strategies, and commensurately to enhancement of transmission performance parameters over a relatively wide range of road speeds and hill grades.
2. Description of the Prior Art
Automatically actuated electromechanical transmissions include actuation software modules of the embedded type, generally including data connection links with engine control modules. Their automatic shift strategies tend to be based on protocols limited to functions of driver throttle demand, engine speed, and torque. Several issues work against ideal performance and operation of transmissions when so limited. For example, the operation of the transmission is essentially a balance or blend between the economic usage of fuel and optimal performance demands. An obvious limitation is that the typical control module has no options with respect to selectively optimizing fuel economy versus optimizing power usage as separate choice modes.
In addition, an approach based upon balancing fuel economy and power optimization targets actually falls short of objectives desired by most fleet operators. To the extent that highway line haul vehicles spend approximately ninety percent (90%) of their operations in upper gear ratios, there are now available transmissions that provide relatively small average ratios steps between the highest gears. Such a transmission is fully described in U.S. Pat. No. 6,085,606, issued Jul. 11, 2000 to Stine et al., and is hereby incorporated by reference. The approach of making the ratio steps relatively small between the highest gears recognizes that in the operation of the vehicle on flat surfaces or relatively small grades, smaller ratios changes can improve overall efficiencies and operating characteristics of the vehicle. On the other hand, where higher hill grades are encountered, a more optimal power mode is normally desirable. An improvement wherein choice of fuel economy mode or performance optimization mode is provided is seen as beneficial, and entirely within the practical limits and/or feasibility of today""s vehicular systems, especially those of on-highway trucks.
The present invention offers an improved operation of a vehicular transmission control module by providing a choice of shift strategies for the operator, particularly as a function of driving conditions encountered. In the described embodiment, two separate shift strategies are presented; one directed to fuel economy, the other to power optimization. The control module is configured to simulate or xe2x80x9cmockxe2x80x9d the performance of a continuously variable transmission in upper gear ratios of the transmission. Thus, the two shift strategies are particularly suitable for use in an electromechanically actuated automotive transmission having reduced ratios steps in its upper ratio ranges.
In one described embodiment, a 12-speed truck transmission consists of a five-speed main section and an auxiliary section including splitter and range sub-sections adapted to provide the twelve ratios. Both strategies are targeted only to upper gear ratios, which represent the ratios experienced in approximately ninety percent (90%) of the operating cycles of on-highway trucks. In the described embodiment, the applicable ratios are gears 7-12, having relatively small ratio step changes between them, and the shift strategies are carried out by embedded software subject to the command of an electronic control module of an associated vehicular engine. Both strategies are operated and measured as direct functions of developed engine power, engine torque, transmission input shaft speed, and road speed.